Originally Posted by
VicMel
Thanks for your detailed response with all of your valid comments. As you say, I believe we, and many other posters are “on the same page”.
Hence my concern:- Because MCAS software was not produced to Level A, it is not assured to be at a high enough standard to allow it to directly control the stabilizer. The risk is that there could be a fault in the software that could cause an erroneous trim condition. The proposed patch may not have any effect on such a software fault.
If I were a betting man, I would put a few pounds on this suggestion. Failure of the AoA sensor seems to being clutched at like the proverbial man and a straw, but I've yet to see anything which confirms this. Let's hope Boeing are also pouring over the code with a very fine toothcomb.
Peter Lemme (Satcom Guru) has also commented on the AoA versus software issue.
(I've posted this previously but it adds context to repost here.)
Ethiopian ET302 similarities to Lion Air JT610Reports from Ethiopian investigators have implicated the same Angle of Attack (AoA) sensor malfunction that was observed on Lion Air. Lion Air captain AoA sensor read about 22 degrees higher than the First Officer AoA sensor (a large bias error). Initial assessment of Lion Air AoA failure modes did not reveal any obvious electrical malfunction that could create the bias. The simplest explanation was that the AoA vane had been bent, causing a gross aerodynamic offset in the readings. If ET302 encountered the exact same offset, with the likelihood of it being bent exactly the same way not being conceivable, some other factor must be in play. For example, the ARINC 429 representation of AoA uses two's complement fraction binary notation (BNR). It is interesting to note that bit 26 represents 22.5 degrees which would be the bit "flipping" between the Captain and F/O AoA values (all other bits would match). Is it possible that the ARINC 429 word is getting corrupted (software defect)? If the ET302 offset was something like 20 or 24, this theory falls apart.
Full post
https://www.satcom.guru/2019/03/ethi...lion.html#more